Bo Jing

Hierarchical porous nitrogen doping activated carbon with high performance for supercapacitor electrodes

Hierarchical porous nitrogen doping activated carbon materials were designed and prepared by carbonization of electrospun composite carbon nanofibers and subsequent chemical activation. The porous carbons were activated by potassium hydroxide (KOH) and the optimal activation weight ratio for carbons was investigated for this process. It is found that activation weight ratios played an important role on the porous structures and capacitive properties. The morphology, pore structure and surface physicochemical properties of the carbon samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption isotherm analysis. The sample with the activation weight ratio of 4 possessed a large 2217 m2 g−1 specific surface area and held a high 1.443 cm3 g−1 volume value as well as a hierarchical porous structure. A symmetrical supercapacitor was fabricated using 6 mol L−1 KOH as the electrolyte and the electrochemical properties were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge–discharge (GCD) and life cycle measurements. The results indicate that the sample with an activation weight ratio of 4 obtained high specific capacitances of 255, 238, 230, 215 and 198 F g−1 at the current densities of 0.2, 0.5, 1.0, 5.0 and 10 A g−1, respectively. Furthermore, the sample materials presented good cycling behavior with respect to the specific capacitance value, which hardly decreased during 8000 cycles. This is considerably promising for this type of porous material to be far-reaching applied in the field of electrode materials for supercapacitors.

Gel electrolytes based on poly(vinylidenefluoride-co-hexafluoropropylene)/thermoplastic polyurethane/poly(methyl methacrylate) with in situ SiO2 for polymer lithium batteries

Gel polymer electrolyte films based on poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF–HFP), thermoplastic polyurethane (TPU) and poly(methyl methacrylate) (PMMA) with and without in situ SiO2 fillers are prepared by electrospinning a polymer solution at room temperature. The electrospun PVDF–HFP/TPU/PMMA blending membrane with 2% in situ SiO2 shows a highest ionic conductivity of 8.5 × 10−3 S cm−1 with electrochemical stability up to 5.9 V versus Li+/Li at room temperature. In addition, it shows a first charge of 168.5 mA h g−1, which is about 99% of the theoretical capacity of LiFePO4; the tensile strength of the PVDF–HFP/TPU/PMMA membrane is 10.8 MPa with elongation-at-break at 86.4%. With the outstanding electrochemical and mechanical performance, it is very suitable for application in polymer lithium batteries.